PurposeDielectric resonator antenna (DRAs) are compact structures that exhibit low coupling between adjacent elements and therefore can be used as MRI transmit arrays. In this study, we use very... Show morePurposeDielectric resonator antenna (DRAs) are compact structures that exhibit low coupling between adjacent elements and therefore can be used as MRI transmit arrays. In this study, we use very high permittivity materials to construct modular flexible transceive arrays of a variable numbers of elements for operation at 7T.MethodsDRAs were constructed using rectangular blocks of ceramic (lead zirconate titanate, epsilon(r)=1070) with the transverse electric (TE)(01) mode tuned to 298 MHz. Finite-difference time-domain simulations were used to determine the B-1 and specific absorption rate distributions. B1+ maps were acquired in a phantom to validate the simulations. Performance was compared to an equally sized surface coil. In vivo images were acquired of the wrist (four elements), ankle (seven elements), and calf muscle (16 elements).ResultsCoupling between DRAs spaced 5mm apart on a phantom was -18.2 dB compared to -9.1 dB for equivalently spaced surface coils. DRAs showed a higher B1+ intensity close to the antenna but a lower penetration depth compared to the surface coil.ConclusionDRAs show very low coupling compared to equally sized surface coils and can be used in transceive arrays without requiring decoupling networks. The penetration depth of the current DRA geometry means they are ideally suited to imaging of extremities. Magn Reson Med 79:1781-1788, 2018. (c) 2017 The Authors Magnetic Resonance in Medicine published by Wiley Periodicals, Inc. on behalf of International Society for Magnetic Resonance in Medicine. This is an open access article under the terms of the Creative Commons Attribution NonCommercial License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited and is not used for commercial purposes. Show less
PurposeTo explore the effect of using extremely high permittivity (epsilon(r)approximate to 1,000) materials on image quality and power requirements of spine imaging at 3 T.Theory and MethodsA... Show morePurposeTo explore the effect of using extremely high permittivity (epsilon(r)approximate to 1,000) materials on image quality and power requirements of spine imaging at 3 T.Theory and MethodsA linear array of high permittivity dielectric blocks made of lead zirconate titanate (PZT) was designed and characterized by electromagnetic simulations and experiments. Their effect on the transmit efficiency, receive sensitivity, power deposition, and diagnostic image quality was analyzed in vivo in 10 healthy volunteers.ResultsSimulation results showed that for quadrature mode excitation, the PZT blocks improve the transmit efficiency by 75% while reducing the maximum 10g average specific absorption rate (SAR(10)) by 20%. In vivo experiments in 10 healthy volunteers showed statistically significant improvements for the transmit efficiency, and image quality. Compared to active radiofrequency shimming, image quality was similar, but the required system input power was significantly lower for quadrature excitation using the PZT blocks.ConclusionFor single-channel transmit systems, using high permittivity PZT blocks offer a way to improve transmit efficiency and image quality in the spine. Results show that the effect, and therefore optimal design, is body mass index and sex specific. Magn Reson Med 79:1192-1199, 2018. (c) 2017 The Authors Magnetic Resonance in Medicine published by Wiley Periodicals, Inc. on behalf of International Society for Magnetic Resonance in Medicine. This is an open access article under the terms of the Creative Commons Attribution NonCommercial License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited and is not used for commercial purposes. Show less
PurposeTo develop a method of suppressing the multi-resonance fat signal in diffusion-weighted imaging of skeletal muscle. This is particularly important when imaging patients with muscular... Show morePurposeTo develop a method of suppressing the multi-resonance fat signal in diffusion-weighted imaging of skeletal muscle. This is particularly important when imaging patients with muscular dystrophies, a group of diseases which cause gradual replacement of muscle tissue by fat.Theory and MethodsThe signal from the olefinic fat peak at 5.3 ppm can significantly confound diffusion-tensor imaging measurements. Dixon olefinic fat suppression (DOFS), a magnitude-based chemical-shift-based method of suppressing the olefinic peak, is proposed. It is verified in vivo by performing diffusion tensor imaging (DTI)-based quantification in the lower leg of seven healthy volunteers, and compared to two previously described fat-suppression techniques in regions with and without fat contamination.ResultsIn the region without fat contamination, DOFS produces similar results to existing techniques, whereas in muscle contaminated by subcutaneous fat signal moved due to the chemical shift artefact, it consistently showed significantly higher (P=0.018) mean diffusivity (MD). Because fat presence lowers MD, this suggests improved fat suppression.ConclusionDOFS offers superior fat suppression and enhances quantitative measurements in the muscle in the presence of fat. DOFS is an alternative to spectral olefinic fat suppression. Magn Reson Med 79:152-159, 2018. (c) 2017 International Society for Magnetic Resonance in Medicine. Show less
Suzuki, Yuriko; Fujima, Noriyuki; Ogino, Tetsuo; Meakin, James Alastair; Suwa, Akira; Sugimori, Hiroyuki; ... ; van, Osch Matthias J. P. 2018
